Fine line print enhancement

Abstract

This discloses an electrophotographic printing machine with circuits to enhance the printing of fine lines, such as lines of a single picture element (pel) in width. Provision is made for broadening such lines in one dimension by adding small "black" areas to each edge of the fine line in order to broaden it. In a second dimension, perpendicular to the first dimension, lines are broadened by placing gray pels next to black pels. The disclosure also discusses specific cases in which it may be considered desirable to inhibit the enhancement signals.

What is claimed is: 
     
       1. An electrophotographic printing machine comprising: drive means;   movable carrier means driven by said drive means;   photoreceptive material mounted on said movable carrier means for cyclic movement through electrophotographic process stations;   charge corona means located at a first station for placing a relatively uniform electrostatic charge on the surface of said photoreceptive material;   exposure means located at a second station for selectively discharging the charged photoreceptive material to cause the formation of a latent image on said material;   toner for developing said image;   developer means located at a third station for applying said toner to said image to produce a developed image;   image receiving material;   transfer means located at a fourth station for transferring said developed image from said photoreceptive material to said image receiving material;   paper storage means for holding a supply of image receiving material;   a finishing station;   paper forwarding means for serially moving image receiving material from said storage means through the transfer station to said finishing station;   control means for operating said exposure means, said control means comprising:   a character generator for producing data signals to drive said exposure means to produce the desired image on said photoreceptive material; and   enhancement means for altering certain of said data signals before presentation of said signals to said exposure means to produce broadened image lines on said photoreceptor where said lines occur in either of two dimensions perpendicular to each other.   
     
     
       2. The machine of claim 1 wherein said enhancement means produces a first type of altered signal to expand said data signals, the expanded signal modulating said exposure means to produce a broadened image line in a first dimension. 
     
     
       3. The machine of claim 1 wherein said enhancement means produces a second type of altered signal which modulates said exposure means to produce an intermediate discharge level adjacent the transition from fully charged levels to fully exposed levels to provide a broadened image line in a second dimension. 
     
     
       4. The machine of claim 2 wherein said enhancement means produces a second type of altered signal which modulates said exposure means to produce an intermediate discharge level adjacent the transition from fully charged levels to fully exposed levels to provide a broadened image line in a second dimension. 
     
     
       5. The machine of claim 2 wherein said enhancement means further includes: means for receiving a stream of data signals representing a first print line;   means for analyzing said data stream to identify data signals representing fine line data, said fine line data signals having a first value level;   means for producing a leading signal of said first value directly leading said fine line data signals;   means for producing a trailing signal of said first value directly trailing said fine line data signals; and   means for combining said fine line data signals with said leading signal and said trailing signal to provide expanded fine line data signals of a first value level within the data signal stream.   
     
     
       6. The machine of claim 5 wherein said expanded fine line data signals are produced for modulating an image one pel in width. 
     
     
       7. The machine of claim 3 wherein said enhancement means further includes: means to store a stream of data signals representing a first line;   means for reading said stored data signals during reception of a stream of data signals representing the second line; and   means for operating upon said data signals representing said first line to produce a separate data signal corresponding to the location of each data signal of a first level in said first line, said separate signals capable of producing a modulated exposure to said intermediate discharge level on said photoreceptive material.   
     
     
       8. The machine of claim 7 further including means for combining said separate data signal with said stream of signals representing said second line before presentation of the second line data stream to said exposure means. 
     
     
       9. The machine of claim 8 further including means for reducing the width of each of said separate signals to a time period less than a full data signal. 
     
     
       10. The machine of claim 4 wherein said enhancement means further includes: means for receiving a stream of data signals representing a first line;   means for analyzing said data stream to identify data signals representing fine line data, said fine line data signals having a first value level;   means for producing a leading signal of said first value directly leading said fine line data signals;   means for producing a trailing signal of said first value directly trailing said fine line data signals; and   means for combining said fine line data signals with said leading signal and said trailing signal to provide expanded fine line data signals of a first value within the data signal stream.   
     
     
       11. The machine of claim 10 wherein said expanded fine line data signals are produced for modulating an image one pel in width. 
     
     
       12. The machine of claim 11 wherein said enhancement means further includes: means to store a stream of data signals representing a first line;   means for reading said stored data signals during reception of a stream of data signals representing the second line; and   means for operating upon said data signals representing said first line to produce a separate data signal corresponding to the location of each data signal of a first level in said first line, said separate signals capable of producing a modulated exposure to said intermediate discharge level on said photoreceptive material.   
     
     
       13. The machine of claim 12 further including means for combining said separate data signals with said stream of signals representing said second line before presentation of the second line data stream to said exposure means. 
     
     
       14. The machine of claim 13 further including means for reducing the width of each of said separate signals to a time period less than a full data signal. 
     
     
       15. The machine of claim 4 wherein said enhancement means further includes: means to store a stream of data signals representing a first line;   means for reading said stored data signals during reception of a stream of data signals representing the second line; and   means for operating upon said data signal representing said first line to produce separate data signals corresponding to the location of each data signal of a first level in said first line, said separate signals capable of producing a modulated exposure to said intermediate discharge level on said photoreceptive material.   
     
     
       16. The machine of claim 15 further including means for combining said separate data signals with said stream of signals representing said second line before presentation of the second line data stream to said exposure means. 
     
     
       17. The machine of claim 16 further including means for reducing the width of each of said separate signals to a time period less than a full data signal. 
     
     
       18. In a printing machine, imaging means for producing an image to be reproduced on work material, control means for operating said imaging means to create the desired pattern on said material, in accordance with image producing data signals, said control means including enhancement means for enhancing the print output of said printing machine by broadening fine lines occurring in either of two perpendicular directions. 
     
     
       19. The machine of claim 18 wherein said imaging means includes light source means and means to direct illumination in a scanning motion across work material comprised of photoreceptive material and wherein said enhancement means broadens fine lines in a direction parallel to the scan direction by modulating said light source means to produce an intermediate discharge level on said photoreceptive material directly adjacent low discharge levels produced in accordance with fine line data. 
     
     
       20. The machine of claim 19 wherein said fine line data, without enhancement, produces a line one picture element in width. 
     
     
       21. The machine of claim 18 wherein said enhancement means broadens fine lines in a direction perpendicular to the scan direction by modulating said light source means to produce expanded picture elements of a low discharge level on said photoreceptive material in accordance with fine line data. 
     
     
       22. The machine of claim 21 wherein said fine line data, without enhancement, produces a line one picture element in width. 
     
     
       23. The machine of claim 19 wherein said enhancement means broadens fine lines in a direction perpendicular to the scan direction by modulating said light source means to produce expanded picture elements of a low discharge level on said photoreceptive material in accordance with fine line data. 
     
     
       24. The machine of claim 23 wherein said fine line data, without enhancement, produces a line one picture element in width. 
     
     
       25. The machine of claim 23 further including a character generator for providing a stream of data signals and wherein said enhancement means is connected to receive the data stream from said character generator and alter selected signals to provide fine line enhancement, the output of said character generator and enhancement means connected to drive said light source means. 
     
     
       26. The machine of claim 25 wherein said enhancement means further includes: means for analyzing said data stream to identify data signals representing fine line data signals having a first value level;   means for producing a leading signal of said first value directly leading said fine line data signals;   means for producing a trailing signal of said first value directly trailing said fine line data signals; and   means for combining said fine line data signals with said leading edge signal and said trailing edge signal to provide expanded fine line data signals of a first value level within the data signal stream.   
     
     
       27. The machine of claim 26 wherein said enhancement means further includes: means to store a stream of data signals representing a first line;   means for reading said stored data signals during reception of a stream of data signals representing the second line; and   means for operating upon said data signals representing said first line to produce separate data signals corresponding to the location of each data signal of a first level in said first line, said separate signals capable of producing a modulated exposure to said intermediate discharge level on said photoreceptive material.   
     
     
       28. The machine of claim 27 further including means for combining said separate data signals with said stream of signals representing said second line before presentation of the second line data stream to said light source means. 
     
     
       29. The machine of claim 28 further including means for reducing the width of each of said separate signals to a time period less than a full data signal. 
     
     
       30. The machine of claim 29 wherein said fine line data, without enhancement, produces a line one picture element in width. 
     
     
       31. A method for broadening the width of fine lines in a printed image produced by an electrophotographic printing machine, comprising the steps of: charging the photoreceptive material of said machine to a first charge level;   utilizing exposure means to selectively discharge portions of said photoreceptive material;   obtaining said selective discharge by modulating said exposure means to discharge said photoreceptive material to a second charge level by exposing said material in discrete picture elements in accordance with a stream of data signals;   altering said stream of data signals in a first manner to produce expanded picture elements in a first dimension to broaden fine lines in said first dimension; and   altering said stream of data signals in a second manner to produce an intermediate charge level on said photoreceptive material in picture elements directly adjacent fine line picture elements in a second dimension perpendicular to said first dimension.   
     
     
       32. The method of claim 31 wherein said step of altering said stream of data signals in a first manner further includes the steps of: identifying fine line data signals;   producing a leading edge expansion of said fine line data signals; and   producing a trailing edge expansion of fine line data signals;   thereby producing expanded data signals with which to modulate said exposure means to broaden said fine lines in said first dimension.   
     
     
       33. The method of claim 31 wherein said step of altering said stream of data signals in a second manner further includes the steps of: storing a first group of data signals representing a first line;   reading said stored signals simultaneously with the reception of a second group of data signals representing a second line; and   operating upon said groups of data signals to produce an altered stream of data signals to produce said intermediate charge level.   
     
     
       34. The method of claim 33 wherein said step of operating upon said groups of data signals further includes the steps of: in said first group of signals, identifying those signals of a value level which will modulate said exposure means to produce said second charge level on said photoreceptive material;   producing a modified signal to replace each of the identified signals in said first group, said modified signals for producing said intermediate charge level on said photoreceptive material; and   combining said modified signals with said second group of signals prior to modulating said exposure means.   
     
     
       35. In a method of enhancing the printing of fine lines by an electrophotographic printing machine which method includes a first group of steps to add gray picture elements directly adjacent picture elements defining a fine line in a first dimension, and includes a second group of steps to expand picture elements defining a fine line in a second dimension perpendicular to said first dimension, the improvement comprising the steps of: inhibiting the output signal of one of the groups of enhancement steps when an expanded picture element coincides with a gray picture element in the same picture element area.   
     
     
       36. In a method of enhancing the printing of fine lines by an electrophotographic printing machine which method includes a first group of steps to add gray picture elements directly adjacent picture elements defining a fine line in a first dimension, and includes a second group of steps to expand picture elements defining a fine line in a second dimension perpendicular to said first dimension, the improvement comprising the steps of: inhibiting the output signals of both groups of enhancement steps when two expanded picture elements coincide with a gray picture element in the same picture element area.